Blown fiber-containing shoe sole and method of making same



Feb. 11, 1958 K. SEIBERLING 2,822,527

BLOWN FIBER-CONTAINING SHOE SOLE AND METHOD OF MAKING SAME Filed May 25, 1955 INVENTOR. THEOPHILUS K. SEIBERLING ATTORNEY United States Patent BLOWN FIBER-CONTAINING SHOESOLE AND "METHODOF'MAKING'SA1\4E" This invention relates to blown tfibencontainir ggshoe sol'es. Thesoles'a're'blown just siiflicientlytotreduce their gravity to about that of water, preferably Slightly lessl than that of water. h may beconsiderably lighter than water. The soles are desig'n'ed particuly fo us o twqrk ng ens s oes, bu ay e e pn q h shq sole. It 7 must have good wear; it must bellight in weig "tlmust b elX b e; A fmus h onl p pmii'e e -(ah coefficientfoft friction); and, to make it most acceptable to the trade, it must havevsuch a cousistencythat' it can be stitched on Lto" a shoe. The sole of this invention possesses all of these desirabl rq e tie n add o ay e mad 5 stantiahthickness without becoming too heavy, aindth is is desirable for several reasons." It' lifts the workman up out of any water, etc. onthe fioor orl ground, andassists ina bsor l'virig "shocks produced by stepping on a stone or other'irregular object. "The" fibers and air cells in thejso'le There are severalnthings required in a shoe s also assistin spreading and absorbing shocks. 1 The air cells also insulatethewearer'from thefheat and coldiof the surfaces on which he stands or Walksf 'Affurther function of the air cells is to reduce the grayity' of thc sole and make it possible to have'the sole or desired fihickne ss, "without its being too heavyf blown solernade' from a rubber composition which does not containfiber is not adapted 'for'sti'tching to the upper portion of a shoe (ordinarily throu'gh'a welt), unlessthe sole is made very stifi. The soft sole ernis'mvemion is made stitchable by the fibers which "prevent the threads used in stitching from cuttingithrough "the r'ubbercomposition or unduly depressingthe rubber composition."" For instance,'if "there are no cords or 'fibersiij' thes'ole, the threads ftend by depressing the sole near the point" of 'the toe to turn the pqin downwardly so that it scufis easily. The edge of the"s"olefis distorted t 'c'ausing an unsightly appearance andaccelerating'wear.

to"20 percent, and may" be 'as much as 30 uneven-40 percent ormore.

The amount ofrubber" may" be just sufficienftohold the fibers togethen' "The preferred fiber source is what is known as cord friction'R This the scrap accumulated during the construction 'of tires from cord fabric. The cord'fabric has a thin coatingof uncured rubber compound frictioiid on to it as amender or thelike. The 'cerasaie twisted fiber'bundl s composed of cotton or of rayontincludipg nylon-etc.)monofilaments; etc; This scrap varies wide} "ly in: comppsition'not only with respect to thecharacter 2,822,627 Patented Feb. 11 1958 2 compoundtarei put on'ztthe different fabric plies used in the: diflerentt' types and kinds 10f tires. Friction s'crap from one source used in the development ofthis invenr-tion; had an average cord content of between 30 and 40 5 .percent,l.buttother scrap will containa higher-or lower 4.66m icontent.

Although large amounts of cord fabric-are employed z-in ithe imanufacture of tires, some-square woven fabric iused. t Erictio'n scrap-which contains such fabric may 10 iibeifemployedl :Qfherrrubber operations produce scraps l-.cont ainirrg titherzfibers; such as' the scrap from the manu- ,:,-faeture 'of 'overshoes'; hose; etc. For the purposes'of invention; friction-scrap which contains cord fibers up'refe'rred ibecause cord-fibers do not disintegrate .dur-

15 "gingstherrriillingt 'operat'ion'lto thedegree that others do. Lis economicaltto usescrap fabric coated with arubbemita. jipossible/gtoifonn the blown soles of this invention from rubber stock to which fresh (unfrictioned) -fiberslafe added. rireshlfibers and scrap fibers may be 20 :mixerlizin'rfth; Ystockiused in carrying out-this invention.

25 zwhiehzcontainszlesscplasticiier. Instead of using plastisGizers,:r-.or;i-in @dditionetb the use of a small amount of -plasticizer,;';softnes'samiay :be imparted by incorporating 'air. ;(or other gas) in therubberstock. ;It is possible-to awhipt air: intotjat latext of rubber or other elastomer, but rithepreferredprocedure-for producingthe-gas-containing ttsolesmfcifihisiihventionxis totincorporate -a gas-forming substance in ithe rubberacompos'ition prior to vulcaniza- (21};213111 their liberate the gasd'uring the vulcanization. ;-:V.arious-: aga's fo'rming '1 compositions are ava-ilable on the :market for thisizpurpose. t-Rubb'er products prepared-in zth'is manner saretrgenerally known as blown products as distinguished fromithe foamed products invvhich air'is twhippeideintosalatxtbfthe rubber or other elastomer. =;'I{oo much air iu.the stock makes it tender,-and sub- 0 ject to scufiing,1particularly'at'th toes and heels. I-lowever, a small amount of air uniformly distributed throughtplltthe stoelt' in small; cells, does: not materially adversely iafiect the stbckiroin the standpointof sciifiirig; "-It makes tlie'stock lighterr in-weight and gives acushioning effect .aanldeinsulation which are veryi desirable.

' u In theublowri: stock ofthis invention-the gas-forming ingredient-is, uniform1ydistributed throughout :the' stock and the cells formed are each complete in themselves and Jiistincbfrom the other-cells. This unicellular structure -is'fdesir1able :or necessary in a sole to prevent the transmission :ofwater, .etc. through the sole. The gas content *Qf:the;stockimay zvarmxbutTin general will range from a minimum vofrperhaps? 2sTor3 percent up to arnaXimum of not over or 01' possiblyf perce'nt. However, tt-he-gas coutenttwillt'depend .upon the gravity desired and thiswill' dependupon-Ihe percentage of heavy compounding ingredientszin the1rubb'er', the amount of fiber's, etc. The sole, maynhavexafgravity greater than that of water. i' lhe grayity .imayi not be substantially greater than that of 0 t 7 3,

-IhSQ1i J11l1Sf =b6ifieXibleIIO be comfortable. Fibers tend-'mmtifien a sole.- By'lcalend'ering a rubber stock whi h tconta'ins"fibers,:the1'fibers are aligned'in the general directipnriu whichltheistock is passed "through the-calender. ,til henstock u'sed:in tithe-blown soles of this invention is Preferablyicut froni' thecalender-ed stock-'in' such away that the aligned fibers lie generally across the finished---sole.- l his -gives flexibility in the lengthwise 0 @iirection of -thesole; "Thisalignment of the fibers also i gives--traction--to-the sole because as the. sole wears "and the-fibers"becomeexposed and then removed from the sole, the resulting cavities lie generally across the sole, giving traction against slippage in the forward and backward directions.

The invention is illustrated in the drawings, in which- Fig. 1 is a bottom view of a sole stitched to 'a shoe; and

Fig. 2 is an enlarged view of the same sole before being stitched to the shoe, with a part of the sole broken away to show the air cells 5 as well as thecords 6. The stitching is identified by the numeral 7.

In determining the hardness of fiber-containing soles with a durometer, if the durometer needle is placed above a fiber a higher reading is obtained than if the needle is located between fibersthat is, away from fibers adjacent the surface of the stock. Thus, the durometer readings give a maximum and minimum hardness which may have a spread of as much as 30 points in Shore A hardness. The hardness of the stock of this invention will preferably have a minimum of 40 and a maximum of 80 Shore A hardness, or thereabout, but will preferably range from about 55 to 65.

It is difiicult to work rubber compositions which con- The friction stock of this invention is tain long fibers. preferably treated by taking a mat of the scrap pieces and running it through a cracker mill (with corrugated rolls) and then running it through a chopper with parallel blades set no more than about i to 1 /2 inches apart. The

resulting fibers are of varying length, but generally not over about 2 inches. Long fibers lying between the knives may be several inches long, and an additional knifing or cracking may be desirable to cut these to short lengths. However, the knifed stock may be added directly to a rubber mill, and if other compounds are to be added they may be compounded with the cracked stock on this mill. Alternatively, the knifed stock may first be sheeted by being run a second time through a cracker to produce a sheet which is readily handled and v The synthetic rubber in the foregoing formula is lowtemperature GR-S. The function of the retarder is to prevent pre-vulcanization. The reinforcing pigment is a hydrated silicon oxide known as Hi-Sil (manufactured by Columbia-Southern Chemical Corporation). The plasticizer may be mineral oil, an ester, or aromatic material such as a coumarone-indene resin, etc.

The foregoing formula is illustrative and is subject to modification as will be readily appreciated by the man skilled in the art.

The compound is prepared on a rubber-compounding mill or in a Banbury or other suitable equipment. The compounded material is then sheeted out on a calender or the like. In sheeting out the compound the fibers are to a considerable extent aligned in the direction in which .the' sheet passes through the mill. This compounded sheet isthen cut into rectangular slugs with the long dimension of the slug perpendicular to the direction of the calender, so that when the slug is placed lengthwise in the molding cavity for a sole, the fibers will be generally aligned across thesole. This makes the sole more flexible in the length- :wisedirection than crosswise.

The compound contains sufiicient blowing agent to produce a relatively light sponge if the sponge rubber is prepared in an unconfined space or in a large cavity. To produce the desired blown sole a slug is used which contains just less than enough of the rubber compound to completely fill the cavity in the unblown, unvulcanized condition. The amount the stock is blown determines the final than the friction scrap, which is black. The following In order to produce a sole of a different color it is desirable to incorporate pigment in additional rubber compound Which contains no fabric, and then mix this pigmented composition with the cut friction scrap on a rubber mill in any desired proportion. The blowing agent may be compounded with this material before it is added to the scrap or in the operation in which it is blended with the scrap. Any required additional compounding ingredients will be added. It is important that the temperature of the stock containing the blowing agent is not raised sufiiciently to release gas from it prematurely.

The following formula is illustrative:

Parts Natural rubber 65 Synthetic rubber 35 Zinc oxide S Stearic acid 3 Flex-cracking antioxidant l gravity of the sole, and, of course, the gravity is also dependent upon the proportion of heavier and lighter ingredients within the stock.

For the manufacture of a sole /2 inch thick, a slug about /1. inch thick is quite satisfactory. The slug is at room temperature when put into the molding cavity, and the cavity is at the vulcanization temperature. The rubber stock quickly softens, and as the mold is closed the slug'is flattened out and tends to fill the cavity, although the cavity is not completely filled until gas has been releasedfrom the blowing agent. The release of the gas starts at a temperature of about 250 to 280 F., depending upon the blowing agent employed. As the gas is released the rubber composition completely fills the mold and becomes unicellular.

Ifthe sole is removed from the mold before the vulcaniizationiis complete, the contained gas will cause the sole to expand to a very appreciable extent. To prevent such expansion the rubber is completely cured within the mold. The cure required depends upon the accelerator, etc. employed in the rubber compound. Generally the rubber will be cured at around BOQ to ,330, and may take from 5 to l5 minutes, as is well known to the man skilled in the .art. -Difl?erent rubber men will-prefer different accelerators, etc., and different cures will be utilized.

The completely cured stock expands somewhat when ,rernoved frorn the mold and then on cooling shrinks a certain amount, due to the decrease in the volume of the vair entrapped in the cells within the sole. By completingthe cure before removing the sole from the mold the ultimate expansion is reduced to not more than about 1 vor 2 percent. To illustrate, werefer to a specific example going composition that is 24 irons thick. 0n removal from the mold the cured sole expands in all three dimensions. The fibers which are generally crosswise of the sole inhibit lateral expansion so that the greatest expansion occurs lengthwise and also vertically. The percentages of longitudinal and vertical expansion are probably approximately equal. The immediate expansion is followed by contraction on cooling. The overall expansion is a measure of the amount of air entrapped within the cells.

The ordinary sponge sole is cemented to the shoe upper. The fibers in the blown sole of this invention prevent the thread used in stitching from cutting or sinking excessively into the rubber and this sole is therefore eminently adapted for sewing to the upper.

Although the description refers more particularly to the use of cords and other fibers-other flexible, elongated, individually distinct elements may be, employed. They are closely distributed within the unicellular rubber in order to accomplish the results described.

What I claim is:

1. A unicellular rubber shoe sole which contains flexible, elongated, individually distinct elements of a length up to not substantially over 1% inches, said elements being closely distributed throughout the sole.

2. The sole of claim 1 in which the flexible elements are cords.

3. The sole of claim 1 in which the flexible elements are, in general, aligned across the sole.

4. The method of making a shoe sole which comprises incorporating a blowing agent and flexible, elongated elements in rubber stock and bringing said elements generally into alignment therein, cutting a slug from the stock with the elements crosswise of the slug, putting the slug lengthwise in the cavity of a mold, closing the mold, and then heating the slug and completing the vulcanization of the rubber in the cavity and releasing gas from the blowing agent while maintaining the mold closed, and thereby forming unicellular gas cells in the stock which cause it to completely fill the cavity.

5. The process of claim 4 in which the flexible elements are cords.

References Cited in the file of this patent UNITED STATES PATENTS 1,137,159 Meyer Apr. 27, 1915 1,249,702 Wiegand et a1 Dec. 11, 1917 1,347,775 Burr et a1. July 27, 1920. 1,457,826 Egerton June 5, 1923 1,884,106 Moran Oct. 25, 1932 1,918,893 Beckmann July 18, 1933 2,168,243 Rollman Aug. 1, 1939 2,374,487 Jayne Apr. 24, 1945 2,382,248 Mason Aug. 14, 1945 2,663,097 Giese Dec. 22, 1953 OTHER REFERENCES Glass Fiber Reinforcement of Foam Rubber," The Rubber Age Synthetic, November 1950, page 330. 

